In what is perhaps the music industry’s worst kept secret, THR has learned definitively that X Factor judge and former Island Def Jam chairman Antonio “L.A.” Reid is headed to Sony Music. He will take on the chairman title at the soon-to-be restructured Epic Label Group, which will encompass Jive Records and reunite Reid with two artists he discovered and developed: Usher and Pink. Sources tells THR the 55-year-old executive is expected to arrive at 550 Madison just after the fourth of July h